As a first step, the limits of current state of the art models were determined to find that even the mature Two Fluid Model (TFM) can already provide industrially interesting simulation results in certain cases featuring dense fluidized beds, larger parti cle sizes and slower reaction rates. Substantial effort was invested in order to form a more fundamental understanding of the grid independence behaviour of TFM simulations, revealing the particle relaxation time as a surprisingly reliable predictor of th e cell size required for grid independence. However, as the particle size was decreased, the fluidization velocity was increased, the bed width was decreased and the reaction rate was increased, the simulation problem rapidly increased in complexity, both due to the fine meshes required and uncertainties related to various closure model coefficients.
For the wide range of cases that will remain out of the reach of the TFM approach for the foreseeable future, four alternative modelling methodologies wer e investigated: 2D simulations, a Lagrangian parcel-based approach, a filtered Eulerian approach and a phenomenological 1D approach. The bulk of work was dedicated to the relatively new Lagrangian parcel-based approach which was thoroughly tested and impr oved by adding the transport of granular temperature and the influence of the full stress tensor on particle motion. Practical experience was gained with the other approaches as well, ultimately allowing for the tabulation of the pros and cons of these ap proaches and the formulation of clear recommendations for future work. Experience suggests that no single approach will be generically applicable over all fluidization cases within the foreseeable future. Modellers should therefore respect the different s trengths and weaknesses of each approach in order to select the most efficient modelling approach for any given application.
A large amount of effort was also dedicated to model validation, both against published experiments and experiments carried ou t within the project. Although a number of unexplained discrepancies remain, comparisons to experiments focussing on hydrodynamics, species transfer and heterogeneous reactions were generally encouraging. Furthermore, experience gained with the operation of the novel reactive unit constructed in this project will be very valuable in directing future reactive validation studies. It was also found that building dedicated experiments was a significantly better investment than the inefficient practice of tryi ng to validate against published experimental data that was not collected for the primary purpose of model validation.
Finally, practical experience was gained with two possible applications of reactive multiphase flow modelling to accelerate the deve lopment of CLC: virtual prototyping of new process concepts and process optimization. In both cases, the fundamental advantages of such a simulation-based process design strategy were found to be highly attractive. Virtual prototyping granted complete cre ative freedom when it comes to the design of new reactor concepts and statistical optimization methods that previously were practically impossible became highly practical.
CLC is a new emerging technology with the potential to reduce the cost of CO2 capture. A novel design, optimum operation and scale-up of the fluidized bed and fast riser reactors in CLC systems significantly depend on fundamental understanding of complex hydrodynamic behaviour in the CLC reactors. CFD holds the greatest potential as a modelling methodology to predict the hydrodynamics and related characteristics of fluidized beds. Numerical modelling of such complex systems is very challenging due to comp lexity of the multiphase flows in the reactors and a substantial number of open questions still exist within the field. This project will develop reactive multiphase CFD models for both the fuel and air reactors of CLC. The granular viscosity, particle-pa rticle collisions, wall interactions, complex turbulence and reaction kinetics of multiphase flows in air and fuel reactors will be extensively investigated in CFD models. The model results will be validated with dedicated experimental work. In particular , advanced experimental techniques will be applied to measure void fractions and velocity profiles inside the 3D beds in reactive conditions (high temperatures, gas mixtures, etc). Axial and radial temperature profiles, gas concentration profiles and inle t/outlet conditions will also be measured for both reactors. In case of any discrepancies between the model and experimental results, 3D discrete hard sphere particle model approach (DPM) will be investigated as a modelling alternative. This type of funda mental knowledge of multiphase reactive fluid dynamic behaviour of the gas-solid flow is essential for advancement of CLC systems through basic research. The project will be conducted at SINTEF Materials and Chemistry, NTNU and Eindhoven University of Tec hnology, The Netherlands.